Contribution of left frontal-motor alpha phase synchronization to semantic inhibition in obsessive–compulsive tendencies

Abstract

Patients with obsessive-compulsive disorder attempt to suppress obsessions and/or compulsions. Although previous psychological research suggests reduced semantic inhibition in such patients, no research has explored the underlying neural mechanisms of semantic control in patients with obsessive-compulsive disorder. In addition to semantic representation, semantic control also generates task-relevant behaviors. Previous research has implicated the left frontal and posterior temporal areas in semantic control; however, no research approaches the dynamic relationships among task-relevant brain areas. To address this, we investigated the phase synchronizations among these areas using time-frequency analysis of data from an electroencephalograph, recorded during a semantic classification task. Participants were healthy patients whose obsessive-compulsive tendencies were assessed using a questionnaire. In this task, when presented with a red colored word, participants were required to classify it into categories as either plants or animals with a keypress (i.e. the classification condition). When presented with a green colored word, participants were required to read it without classification (i.e. the inhibition condition). The behavioral results showed that the semantic negative priming (i.e. the increase in reaction time to the word included in the previously inhibited category) was negatively correlated with obsessive-compulsive tendencies. Electroencephalograph results showed that the left frontal-motor alpha phase synchronization under the classification condition was significantly higher than under the inhibition condition. This phase synchronization under the inhibition condition was positively correlated with obsessive-compulsive tendencies. These results suggest that a dynamic link between the left frontal and motor areas may reflect reduced semantic inhibition in individuals with stronger obsessive-compulsive tendencies.